Lead shift mechanism



L. F. DORAN LEAD SHIFT MECHANISM April 2s, 1964 3 Sheets-Sheet 1 Filed March 23, 1961 INVENTOR.

EO @0R/71V April 28, 1964 1 F. DORAN LEAD SHIFT MECHANISM 3 Sheets-Sheet 2 Filed March 23, 1961 April 2s, 1964 L. F. DORAN LEAD SHIFT MECHANISM Filed March 23, 1961 Q QP No wn .ww a www. A a Oh U M United States Patent O 3,130,522 LEAD SMT MECHANSM Leo F. Doran, Ciawson, Mich., assigner to Beaver Precision Products, Inc., Clawson, Mich., a corporation oi' R/lichigan Filed Mar. 23, 3196i, Ser. No. 97,889 10 Claims. (Cl. 51--95) This invention relates to machines for producing threads in cylindrical work-pieces, and more particularly to a mechanism for axially shifting a work piece on a thread grinding machine.

In certain classes of thread grinding work it is desired to form a thread of a given pitch throughout the axial length of the thread except for one or more portions in which it is desired to have a transitional thread having a pitch which varies from that of the major portion of the thread. One purpose of such transitional threads is to oifset the uniformly threaded portions from one another without affecting the pitch of such portions.

@ne application of such threads is on a screw-nut assembly of the recirculating ball type. In order to preload such assemblies it is not uncommon to form the helical thread groove in the nut in two sections having uniform pitch but offset from one another. With such an arrangement the balls interengaging the nut and screw will bear against one side of the helical thread groove at one section of the nut and against the opposite side of the thread at the other section of the thread on the nut.

This oifset between the two thread sections may be produced by grinding a uniform thread in one portion, stopping the grinding operation and then shifting the lead-screw a distance corresponding to the desired ottset by means of a hand operated element. Then the grinding operation is resumed so as to grind the same thread on the following portion of the work. However, such a manual shifting procedure is time consuming and subject to human error in determining both the position and setting of the manual control elements.

Accordingly, it is an object of the present invention to provide an improved mechanism for a work forming machine which automatically produces a selected amount of axial oifset in the work at any axial location therein as the work moves relative to the work forming element of the machine.

Another object is to provide an improved lead shift mechanism for a thread grinding machine which automatically provides a predetermined otfset between successive uniformly threaded portions of the work.

A further object is to provide an improved lead shift mechanism which is simple to construct, which is readily installed on conventional thread grinding machines, and which is accessible and easy to operate.

In the accompanying drawing:

FIG. 1 is a fragmentary elevational view of a thread grinding machine illustrating principally the headstock thereof in which a lead shift mechanism is incorporated in accordance with the invention;

FIG. 2 is an enlarged elevational view of the chuck holder of the invention illustrated partially in longitudinal center section;

FIG. 3 is a fragmentary elevational view on the same scale as FIG. 2 of the rear portion of the spindle train and cam elements of the lead shift mechanism shown partially in longitudinal center section;

FIG. 4 is a fragmentary end elevational view of that portion of the lead shift mechanism accessible at the rear of the headstock of the machine;

FIG. 5 is a fragmentary elevational view at the opposite side of the machine from that shown in FIG. l

showing the cam actuating linkage of the lead shift mechanism;

FIG. 6 is a greatly enlarged fragmentary longitudinal sectional view or a ball and screw combination illustrating the two uniformly threaded portions offset from one another by a transitional thread produced by a thread grinding machine equipped with the invention; and

FIG. 7 is a side elevational View, somewhat schematic, of the thread grinding machine.

Referring in more detail to the accompanying drawing, FIG. l shows a portion of a conventional thread grinding machine including a supporting frame i0 havinC a pair of ways i2 on which a headstock 14 is slidabiy supported for rectilinear movement as indicated by arrow i3. A grinding wheel i6 is mounted on a wheel spindle i8 which is rotated in xed axial position by a suitable mechanism incorporated in a spindle head 2d of the thread grinding machine. Rectilinear movement of headstoek le on ways l2 is produced by a conventional lead screw mechanism indicated schematically at i3, the lead screw thereof being operable in a known manner to provide predeterrmined rates of axial feed of the work relative to grinding wheel i6.

A conventional chuck 22 is detachably supported on a chuck holder 2d provided in accordance with the invention and which is in turn affixed by an adapter 26 included therein to a face plate 28 of headstock 14. A suitable source of rotary power 27 is connected via a gear drive 29 mounted on headstock le which rotates [ace plate Z3 to thereby produce rotation of a work-piece 3d received on the forward end of chuck 22. Chuck holder 24 is shown in more detail in FG. 2, wherein work-piece 3@ is indicated diagrammatically as are grinding wheel i6, spindle i8, chuck 22 and face plate 2S.

Adapter 25 of chuck holder 2d has an annular mounting plate 26a which is bolted to face plate 28. Adapter 26 also has an integral hollow hub portion 26b with an annular ange 26C spaced axially from harige 26a. A sleeve 32 is slidably received in a central axial bore 26d of adapter Z6. Sleeve 32 has an annular, integral iiange 32a of the same outer diameter as flange 26C which is adapted to abut there against. Flanges 26C and 32a each have four holes 34 and 35 respectively which are circumferentially arranged at intervals therein and adapted to individually receive a cap screw 36 therein. Holes 3d are enlarged in diameter so as to form a chamber 34a which extends axially inward from the rear face of fiange 26e for individually receiving a compression coil spring 3S. Cap screw 36 carries metallic and iiber washers i6 and d8 respectively adapted to seal lubricating fluid in chamber 34a and to engage the outer end of spring 33. rThus, screws 36 and springs 38 provide a resilient connection between anges 32a and 26e which permits limited sliding movement of sleeve 32 relative to adapter 26 while also transmitting torque therebetween.

An annular collar Sii surrounds both flanges 26e and 32a but it is lfastened only to flange 2de as by screws Stia. A plurality of keys 51 provide a rotary, axially slidably driving connection between collar Sti and iiange 32a. Collar 50 has an internal annular shoulder 52 the inner radial face of which is spaced a suiiicient distance from flange 26e to allow movement of lla-nge 32a therebetween. A face plate 54 is fastened by cap screws 56 to iiange 32a, plate 54 having a rearwardly extending cylindrical boss 54a which ts between shoulder '52 or" collar Sti and the forward end of sleeve 32. Since the outer peripheral surface of boss 54a of plate 54 slides against the inner peripheral surface of shoulder 52 in accordance with movement of sleeve 32, provision is made for lubricating these surfaces via an oil fitting 5S. Suitable sealing members such as O-rings 60 and 62 are provided to prevent escape of lubricating iiuid. lFace plate 54 of the chuck holder 24 is provided with suitable slots, keyways,` or other meanslnot shown) for mounting the conventional chuck 22. It will be seen that by reason of keys 51 and screws 56 chuck 22 and workpiece 3l) held thereby are rotated by chuck holder 24;, but may shift axially for a limited distance against the pressure of springs 33 if a suitable force is exerted on sleeve 32..

Referring to IFG. 3, sleeve 32 extends through face plate 28 and into headstock 1d where it is coupled at the rear end thereof by a coupling collar `dfito one end of an extension sleeve 65. The other end of sleeve 56 slides in a flanged bronze bushing 67 litted within the inner race of a ball bearing assembly 6d which is in turn mounted in a coolant head 7d located at the rear of headstock 14. Coolant head 7i) has a passage 72 for supplying liquid coolant to a plurality of apertures 74 provided in sleeve 66, sleeves 66 and 32 forming a conduit 75 for carrying the coolant under pressure to the interior of the workpiece 39 via chuck 22.

ln accordance with the invention the outer end of sleeve 165 projecting beyond bearing assembly `6? is internally threaded to receive an externally threaded cap plug 76 which in turn threadably receives a clamping nut 78. Cap plug 7d has an axial bore 76a internally threaded at the inner end thereof to receive a screw plug 39 which seals bore 76a from coolant conduit 75, and which also serves as a seat for a helical compression spring E52 received in bore 76a of cap plug 76. Spring S2 seats at its other end against a hardened steel bearing ball 8d which is received in a semi-spherically shaped recess `formed in plug 76 co-axial with bore 76:1. A disc 77 having a center hole with a `diameter smaller than the diameter of ball diiis screwed to the outer face of plug 7 6 in order to retain the ball in its seat in plug 76.

lReferring to FlG. l as well as 4to FlG. 3, a cylindrical cam 85 is positioned to engage ball iid so as to determine the axial position of sleeves 65 and `32, and consequently the axial position of workpiece 36 relative to headstock 14. Cam d6 includes a pair of cylindrical bosses Sdu and `Sb which extend from a central cam disc Sec. An axial bore extends through cam Se which receives a cam mounting shaft SS having a -key slot 38a in which a key S9 is inserted for connecting cam 35 to shaft S8. Shaft vSi?, is journal ed in a pair of parallel and rearwardly extending arms 91351 of a pair of mounting brackets 9i) by means of a pair of ball bearing assemblies 92 supported therein. `Mounting brackets 9b are -bolted to the rear face of coolant head itl and are positioned so that the axis of shaft S8 intersects the co-axes of bearing ball @-4 and sleeves 66, 32.

Cam disc '86C is machined to provide peripheral camming surfaces for engaging bearing ball Se. As shown in FIG. 3 approximately half the circumference of cam disc Soc is reduced in diameter to provide a peripheral cam surface 96 the radius of which is on the order of .050 inch less than that of peripheral cam surface 93. Hence it will be seen that rotation of cam disc Soc from its position as shown in FIG. 3 to a position where the smaller radius surface $6 is contacted by ball 34 allows sleeves 66 and 32 to shift axially to the left by an amount corresponding to this difference in radii of cam surfaces 9d and Referring to FIGS. 4 and 5, cam Se is rotated by means of a linkage connected between supporting frame 1li of the thread grinding machine and the cam. This linkage includes a crank arm 1d@ non-rotatably aixed to the extended end of cam lshaft 88 by a key 1112 and set screw 1113. The lower end of crank arm 16) has a series of longitudinally spaced holes 1M one of which receives a pin 1% having a roller `1113 thereon positioned to ride in a Vertical slot 119 of a vertical plate 112. `Plate 112 is secured at its lower end by a cap screw 114 which lextends through a horizontal slot 112a in the plate and is threadably received in one of a series of threaded holes 116 provided in a mounting bar 118. Mounting bar 11g is bolted to the side of supporting -frame `1t!" of the thread grinding machine and extends beyond the end thereof as more clearly seen in FIG. l. Thus mounting bar 118 and plate 112 remain xed in position while cam S6 and cam mounting shaft 8S move relative therelto in accordance with the rectilinear movement of headstock 141;. A keyway connection .119 between plate 112 and mounting bar 118Vassures Vertical alignment of Slot 11@ in plate 1.12 at all times. As the upper endof crank arm 169 moves horizontally along with shaft `Sli, arm 169 pivots about pin 166 while roller 168 moves vertically in slot 11% to compensate for the horizontal movement of the upper end of the crank arm. This pivotal movement of crank arm 10i) causes cam 86 to rotate so that its angular position is a function of the relative position of headstock 14 and hence workpiece 30 with respect to frame 1li and grinding wheel 16.

The above described lead shift mechanism of the in vention, comprising chuck holder 24, cam S6, and the cam actuating and follower elements, may be embodied in a conventional internal thread grinding machine for the preferred purpose of grinding the internal threads of a ball screw assembly such as that partially shown in FIG. 6. As is known in the art, such assemblies comprise an externally threaded shaft 121) which is received in an internally threaded cylindrical nut 122. The helical threads or grooves of each of these parts are of semicircular shape in cross section and adapted to receive a plurality of bearing balls 124 therein. Bearing balls 124 run in the respective threads as the shaft and nut are rotated relative to one another to provide an antifriction couplinfy therebetween. The ball screw assembly also includes two external tubes 126 and 123 which are mounted on nut 122 and connect therethrough with the external threads of nut 122 so as to provide a return conduit for those bearing balls 124i running in the threads located bett een the connecting ends of the conduits. Thus two closed circuits are formed, one circuit including threads 122e of nut 122 located in portion A and the other including threads 1221) located in the portion B of the assembly.

In order to prevent play or undesirable axial shifting between shaft 12d and nut 122, the assembly is preloaded by axially oifsetting threads 12211 by a predetermined amount, for example .010 inch, with respect toV threads 12201 while keeping the pitch of these spaced-apart threaded portions the same. This offset between portions A and B causes the bearing balls 124 to be loaded in opposite directions in the respective portions A and B which effectively takes up the slack in the coupling. The lead shift mechanism of the present invention automat- :'cally establishes the desired offset between threaded portions A and B as the workpiece 30 moves relative to grinding wheel 16. In the process of shifting the travel of workpiece 3d in accordance with the invention a transitional thread is formed in the intermediate portion C, but since bearing balls 124 do not run in the intermediate portion its pitch variation does not affect the operation of the ball screw assembly.

To set up the leaf shift mechanism of the thread grinding machine, assuming it is desired to grind workpiece Btl into nut 12,?. of the above described ball screw assem-V bly, threaded plug 76 is axially adjusted until cam follower ball l just touches the larger diameter surface 9S of carn Se when flange 32a of chuck holder 24 is fully retracted by springs 33. Headstock 14 is then shifted on ways 12 towards spindle head 2i) so that the desired location of the beginning of the transitional thread portion C adjacent threaded portion B is opposite grinding wheel 16. Slotted plate 112 is then shifted along mounting bar 11d so as to rotate cam 86 to the angular position where the beginning of the transition point between low and high surfaces 96 and 9S on the cam 86 is aligned adjacent ball 84 (FIG. 3). Cap screw 114 is then tightened to lock plate 112 in this position. Plug 76 is then rotated to cause movement of plug 76 to the left as viewed in FIG. 3. Since bearing ball 84 is still abutting the high surface 98, this adjustment of plug 76 will cause sleeves 66, 32 to move to the right, thereby displacing the forward portion of chuck holder 24 from adapter 26 against the action of springs 38. The amount of axial adjustment of plug 76 corresponds to the axial offset desired in the ball screw assembly, in this case .010 inch. After plug 76 is thus set, clamping nut 78 is tightened against the end of sleeve 66 to maintain the desired setting. Headstock 14 is returned to the left (as seen in FIG. l), causing crank arm 160 to rotate cam S6 so as to bring the low side 96 thereof opposite ball 84. As ball 84 rolls off high side 98 and over the transition surface of the cam, the springs 3S of chuck holder 24 cause sleeves 32, 66 to move to the left until flange 32a again abuts adapter flange 26C. The machine is now ready for operation.

In operation, the thread in portion B is ground by grinding Wheel 16 as headstock 14 moves towards spindle head 2t). During this movement, crank arm 1% is being pivoted by the relative motion between cam shaft S8 and plate 112, causing low side 96 of cam 86 to rotate past bearing ball 84. It is to be understood that due to the .050 inch difference in diameter between the high and low sides of the ca m there is no contact between bearing ball 84 and low side 96. When workpiece 3d has moved to the point where grinding wheel 15 enters intermediate portion C, cam 86 has been rotated so as to bring the transition portion thereof in contact with ball 84. Further movement of headstock 14 towards spindle head 29 causes high side 98 of cam 86 to be rotated against ball 84, thereby camming sleeve 66, 32 to the right and causing workpiece 39 to be shifted to the right. This shift is additive to the motion imparted by the lead screw mechanism to headstock 14, and thus a transitional thread having a larger pitch than threads 122b is ground in intermediate portion C during this transition from an unengaged position of ball 84 to its position of rolling contact with high side 9S. Once the transition is accomplished, workpiece 30 again is advanced at the rate determined by the lead screw mechanism so that threads 122er ground in portion A are of the same pitch as those ground in portion B but are offset therefrom by the predetermined axial offset adjustment of .010 inch.

It is to be understood that the setup of the lead shift mechanism of the invention may be reversed from that described above if it is desired to produce a subtractive effect at a particular point in the travel of headstock 14. This may be accomplished by reversing the angular position of cam 85 so that during the portion of travel of headstock 14 in which threads 122]; are being ground, ball 84 is riding against high side 98. Then at the transition point between the high and low surfaces 98 and 96, ball 84 would roll o the high surface thereby permitting sleeves 66, 32 and hence chuck 22 to shift to the left in accordance with the offset adjustment of plug 76. Other combinations of additive and subtractive compound motions may be produced by variations in the peripheral contour of cam 85 if such effects are desired in particular applications.

It will now be apparent that the above described lead shift mechanism of the invention provides an easily constructed attachment for installation in a conventional thread grinding machine as well as in other machine tools in which relative motion occurs between the workpiece and a cutting tool. The cam linkage members comprising bar 118, plate 112, and crank arm 11h) as well as cam S6 and its mounting bracket 9d are easily installed at the rear of the thread grinding machine where they are readily accessible for adjustment and replacement. Likewise, the setup of the lead Shift mechanism is accomplished at this convenient location without disassembling or removing any portions of the machine. The cam linkage is adjustable over a wide range due to the provision of the series of holes 104 in crank arm 10i) and the slot 112a in plate 112. Moreover, cam 86 may be readily disconnected by screwing plug 76 fully into sleeve 65 when it is desired to produce a thread with no offset. The provision of bearing ball 84 as a cam follower furnishes a highly eicient universal coupling between cam 86, rotating about an axis perpendicular to the plane of the drawing, and sleeve 66, which is rotating about an axis at right angles thereto.

I claim:

1. The combination comprising a support, a headstock movable in a rectilinear direction on said support, means for moving said headstock in said direction at a uniform rate, a rotatable work supporting spindle carried by and journalled in said headstock and shiftable axially relative thereto in said rectilinear direction, means for rotating said spindle in timed relation to the rectilinear speed of said headstock, a cam movably mounted on said headstock and bodily movable therewith, cam follower means operatively connecting the cam and spindle for shifting the spindle axially on the headstock in response to movement of said cam relative to said headstock, said cam comprising two surfaces connected by a step portion and being designed such that the spindle is shifted axidly on the headstock only when the cam follower means traverses said step portion and means for moving the cam in timed relation to the movement of the headstock on said support.

2. In a thread grinding machine, the combination of a support having way means, a headstock mounted for linear movement along said way means, means for moving the headstock along said ways at a uniform rate, rotatable spindle means carried by and journalled in said headstock and being provided with chuck means for holding a workpiece to be threaded, said spindle means being axially shiftable on said headstock, a cam carried by and journalled on said headstock, said cam having two surface portions spaced radially unequal distances from the axis of rotation of said cam and connected by a radial step portion, biasing means for urging said spindle means axially on the headstock toward said surface portions of said cam, said cam surfaces being shaped such that said spindle means is actuated axially on and relative to said headstock only when the spindle is engaged by the step portion of said cam, and lever means connecting said support with said cam so as to rotate said cam in response to axial movement of said headstock along said way means to thereby shift the axial position of the work piece relative to said headstock in accordance with the relative position of said headstock on said support.

3. In a thread grinding machine, the combination of a support having ways thereon, a headstock mounted for rectilinear movement along said ways, rotatable spindle means journalled on said headstock and provided with chuck means for holding a work piece to be threaded, said spindle being axially slidable in said headstock, a cam journalled on said headstock and movable therewith along said ways, said cam having two surfaces connected by a radial step portion, each of said surfaces having a constant radius which is different from the radius of the other cam surface, said spindle having a cam follower thereon located on the axis thereof, means biasing said spindle axially in a direction to interengage said cam follower with said cam surfaces whereby the spindle is actuated axially relative to the headstock only when the radial step portion of the cam surfaces rotates past said cam follower and means interconnecting said cam and support for rotating said cam in timed relation to the axial movement of the headstock along said ways.

4. The combination called for in claim 3 including means for adjusting the position of the cam follower axially of the spindle to vary the extent of axial movement of the spindle in response to interengagement of the cam follower with the step portion o the cam.

5. In a thread cutting machine, the combination including support means for operably carrying cutting tool means, headstock means on said support means including axially shiftable spindle means carried thereby for supporting a work piece, rotating means operable to produce relative rotation between the cutting tool means and the work piece, feeding means for producing uniform relative axial movement between said support means and said headstock means whereby the Cutting tool means engages and removes material from the work piece to form a thread of a given pitch therein, cam means movably supported on said headstock means, said cam means having one cam surface uniformly spaced from a reference point about which the cam moves and a second cam surface connected with the first cam surface by means of a step surface which is adapted, when the cam is moved about said reference point, to engage and thereby axially shift said spindle means a predetermined amount relative to said headstock means as said cam means moves relative thereto, and cam driving means coupled between said supf port and headstock means for translating relative movement therebetween into movement o1c said cam means whereby said step surface of said cam means causes an axial shift of the work piece relative to said headstock means at a predetermined point in the relative positions of said support and headstock means thereby causing one portion of the thread being formed to be axially otset from another portion thereof.

6. The combination comprising a support, a headstock movable at a uniform rate in a rectilinear direction on said support, a rotat ble work supporting spindle journalled in and carried by said headstock and shiftable axially relative thereto in said rectilinear direction, a cam journalled on and carried by said headstock, a cam follower operatively connecting the cam with the spindle for shifting the spindle axially relative to the headstockV in response to rotation of the cam and lever means interconnecting said cam and said support for rotating the cam in response to axial movement of the headstock on said support.

7. The combination called for in claim 6 including a pivot support on said support to which said lever means are pivo-tally connected.

8. The combination called for in claim 7 including means for adjusting said pivot support in a direction parallel to the direction of movement or" the headstock on the support.

9. The combination called for in claim 7 wherein said lever means comprise a lever non-rotatably connected with said cam, a support plate on said support having a vertical guideway therein and pivot means on said lever.

shiftable vertically in said guideway in response to relative movement between the headstock and the support.

10. The combination called for in claim 9 including means enabling shifting of said support plate by small increments in a direction parallel to the direction of movement of the headstock on the support.

References Cited in the le of this patent UNITED STATES PATENTS 176,250 Taber Apr. 1b, 1876 312,401 Stetson Feb. 17, 1885 FOREIGN PATENTS 843,825 Germany July 14, 1962 

5. IN A THREAD CUTTING MACHINE, THE COMBINATION INCLUDING SUPPORT MEANS FOR OPERABLY CARRYING CUTTING TOOL MEANS, HEADSTOCK MEANS ON SAID SUPPORT MEANS INCLUDING AXIALLY SHIFTABLE SPINDLE MEANS CARRIED THEREBY FOR SUPPORTING A WORK PIECE, ROTATING MEANS OPERABLE TO PRODUCE RELATIVE ROTATION BETWEEN THE CUTTING TOOL MEANS AND THE WORK PIECE, FEEDING MEANS FOR PRODUCING UNIFORM RELATIVE AXIAL MOVEMENT BETWEEN SAID SUPPORT MEANS AND SAID HEADSTOCK MEANS WHEREBY THE CUTTING TOOL MEANS ENGAGES AND REMOVES MATERIAL FROM THE WORK PIECE TO FORM A THREAD OF A GIVEN PITCH THEREIN, CAM MEANS MOVABLY SUPPORTED ON SAID HEADSTOCK MEANS, SAID CAM MEANS HAVING ONE CAM SURFACE UNIFORMLY SPACED FROM A REFERENCE POINT ABOUT WHICH THE CAM MOVES AND A SECOND CAM SURFACE CONNECTED WITH THE FIRST CAM SURFACE BY MEANS OF A STEP SURFACE WHICH IS ADAPTED, WHEN THE CAM IS MOVED ABOUT SAID REFERENCE POINT, TO ENGAGE AND THEREBY AXIALLY SHIFT SAID SPINDLE MEANS A PREDETERMINED AMOUNT RELATIVE TO SAID HEADSTOCK MEANS AS SAID CAM MEANS MOVES RELATIVE THERETO, AND CAM DRIVING MEANS COUPLED BETWEEN SAID SUPPORT AND HEADSTOCK MEANS FOR TRANSLATING RELATIVE MOVEMENT THEREBETWEEN INTO MOVEMENT OF SAID CAM MEANS WHEREBY SAID STEP SURFACE OF SAID CAM MEANS CAUSES AN AXIAL SHIFT OF THE WORK PIECE RELATIVE TO SAID HEADSTOCK MEANS AT A PREDETERMINED POINT IN THE RELATIVE POSITIONS OF SAID SUPPORT AND HEADSTOCK MEANS THEREBY CAUSING ONE PORTION OF THE THREAD BEING FORMED TO BE AXIALLY OFFSET FROM ANOTHER PORTION THEREOF. 